Multi-beam satellite systems routinely use antenna far field patterns and frequency/polarization or color reuse plans to provide discrimination between signals from other beams. Reuse of frequency/polarization allocations over the multiple spot beams generates co-channel interference among adjacent beams. Separating the frequency/polarization resource into multiple separate colors and using a multi-Color reuse plan provides discrimination between signals from other beams. An available frequency spectrum is divided into one or more frequency sub-bands. Some systems also use orthogonal polarizations to provide discrimination between signals. The colors of a reuse plan are mapped/assigned to the frequency sub-bands and one of the, possibly two, polarizations in use.
However, not using all the resources by dividing the frequency spectrum into sub-bands and/or polarizations reduces the beams capacity. There is a need to more efficiently utilize the frequency spectrum and/or polarization in multi-beam systems.
FIG. 1 illustrates a prior art beam laydown pattern with a 4-color reuse plan for a multi-beam satellite, according to various embodiments.
FIG. 1 illustrates a reuse plan combining signal polarization and non-overlapping frequency spectrums to create a 4-color reuse plan 100. In the example, the four colors (hashing in FIG. 1) correspond to four different frequency/polarization allocations. In FIG. 1, an available frequency spectrum is divided into two frequency sub-bands—F1 and F2—and each sub-band is assigned/mapped to a different color, and two orthogonal polarizations are assigned/mapped colors to provide the two other colors in the 4-color reuse plan. A service or coverage area 114 may be divided into cells. Multi-beam satellites typically illuminate multiple hexagonal cells within a service area 114. In exemplary embodiments, a cell 102 may be illuminated by a far field beam pattern using a right hand circularly polarized (RHCP) frequency spectrum such as 18.3 GHz to 18.8 GHz along with a cell 104 which may be illuminated by a far field beam pattern that uses a left hand circularly polarized (LHCP) for the same frequency spectrum, i.e., 18.3 GHz to 18.8 GHz. Furthermore, a cell 106 may be illuminated by a far field beam pattern using a RHCP frequency spectrum in a different frequency spectrum such as 19.7 GHz to 20.2 GHz, along with a cell 108 which may be illuminated by a far field beam pattern that uses a LHCP frequency spectrum in the same spectrum, i.e., 19.7 GHz to 20.2 GHz. A multi-beam satellite implementing a reuse plan may arrange the two polarizations in separate alternate rows, for example, a LHCP row 110 and a RHCP row 112. The alternate rows may reduce the interference between cells using the same circular polarization.
A three-color or seven-color reuse plan, each of which uses both polarizations, is also known. It is possible to tessellate a desired coverage area, such as, earth's surface, using an N-color reuse tessellate where N is any positive natural number. Without limitation, when polarization diversity is used, N is an even number.
In satellite communications, the frequency spectrum between 18.3 GHz to 18.8 GHz and 19.7 GHz to 20.2 GHz is allocated to the geostationary Fixed Satellite Service (FSS) on a primary basis in the United States. See, for example, FCC Online Table of Frequency Allocations, 47 C.F.R. §2.106. Allocations of frequency bands vary elsewhere and may differ in the future. The methods described in these teachings are extensible to other allocations.